A recent renewed interest in coal mining has once again brought out the salient limitations in current procedures for mining coal. Specifically, the most nonproductive segment of time within the coal mining process is associated with roof bolting. The time consumed during this necessary process far exceeds, in proportion, any other time segment dedicated to the other details incorporated within the mining of coal. This delay in the advance of underground continuous mining equipment represents a reduction in mine productivity. Moreover, the instability of the drilling process itself is reflected in the myriad of problems associated with the drilling of roof bolt holes. Specifically, the melting of solder holding the carbide cutting tip on the drill bit, the bending of the drill steel as well as the total lodging of the drill steel within the hole have all resulted in wasted time as well as expense.
The major delay in roof bolting stems from the time consumed in drilling holes for roof bolts. With the present roof drilling machines, the operator utilizes a "feel" of vibration and visual estimates of roof drill penetration rates to adjust the thrust and torque input into the drilling system. While such a nonscientific system produces "adequate" results, the amount of delay in the time consumed in roof hole drilling suggests otherwise. This delay is especially important in other "long" drilling applications. In an ideal situation, the advance of the roof drill into the rock or medium being drilled should be maintained at a maximum penetration rate at all times. It should be obvious from past performances that this optimization has not been obtained.
The specific causes which have resulted in the time consumption inherent in roof bolt drilling comes from an assumed, but incorrect, presumption that roof bolt hole drilling is an art and not a science. This is substantiated in part by the present-day thought that the best roof bolt hole driller is the one man who has the best "feel" for the progress and vibration of the drill and drill steel into the rock. It has recently been determined that the maximized penetration rate of a drill and associated drill steel into any medium being drilled, whether that medium be limestone, sandstone or coal itself, is susceptible to a scientific and logical set of parameters and control algorithms which do in fact result in an optimized rate of penetration into the medium being drilled.
While a variety of prior art is available in this area, none fully appreciate the use of drilling parameters and the values of the drilling parameters which may be manipulated in a specific manner in order to accomplish a maximized penetration rate of the drill into the medium.